The present invention relates to a switching device suitable for use as switches for a vehicle, such as a window regulator switch and a sunroof switch.
A conventional switching device for such purposes is shown in FIGS. 5A and 5B. This switching device is operated by a knob 21. The knob 21 is operated to turn an operating arm 22 attached to the knob 21 on a shaft 23 to make the edge 24a of a card 24 connected to the operating arm 22 and fixed to the core shaft 25 of a solenoid 25 press the movable contact 26a of a transfer contact 26 or the movable contact 27a of a transfer contact 27. When the knob 21 is turned in a counterclockwise direction as viewed in FIG. 5A, the break contact 26b of the transfer contact 26 is opened and the make contact 26c of the same is closed.
As shown in FIG. 5B, the switching device is provided with a detent 28 essentially consisting of a pressing member 28a fitted in a bore formed in the operating arm 22, and a spring 28b provided in the bore of the operating arm 22 so as to press the pressing member 28a against a detent groove 28c to retain the knob 21 at a neutral position.
When the make contact 26c is closed, a current supplied from a power supply 31 flows via the make contact 26c, a diode 32 and a control circuit 33 through the coil 25c of the solenoid 25 and flows also via the make contact 26c and the break contact 27b through a load 34, such as a motor, as shown in FIG. 6. When the coil 25c is thus energized, an attraction is generated between the core 25d and yoke 25b of the solenoid 25. However, when the gap between the core 25d and the yoke 25b is large, and while the attraction is smaller than the sum of the resilience of the movable contact 26a and the retaining force of the detent 28, the core 25d returns to a neutral position to interrupt the supply of current to the load 34 and the coil 25c when the knob is 21 is released. Thus, such a knob operating mode makes the switching device function as a momentary switch manually operated by the knob.
When the knob 21 is operated further to reduce the gap between the yoke 25b and the core 25d after supplying a current to the coil 25c and the load 34, the attraction generated between the yoke 25b and the core 25d exceeds the sum of the resilience of the movable contact 25a and the retaining force of the detent 28, so that the core 25d is attracted to the yoke 25b. Consequently, the current is supplied continuously to the coil 25c and the load 34 after the knob 21 has been released. Thus, such a knob operating mode makes the switching device function as a latching switch. For example, when the control circuit 33 detects an overcurrent which flows when the load 34, such as a motor, is driven excessively, the control circuit 33 interrupts the current supplied to the coil 25c and unlatches the switching device automatically. It is also possible to unlatch the latched switching device by manually operating the knob 21 against the attraction of the solenoid.
In this conventional switching device, the knob is returned automatically to the neutral position when the knob is released in the manual operating mode, whereas the knob is not returned to the neutral position in the automatic operating mode until the automatic operating mode is accomplished even if the knob is released. Accordingly, when the switching device is mounted on a vehicle, in which the operating knob of the switching device is buried substantially in a control panel to avoid the erroneous operation of the knob or in view of the aesthetic appearance of the control panel, this conventional switching device is unsatisfactory in accessibility.